1. The Field of the Invention
The present invention pertains to fibers comprising an alloy of a polyolefin and a polyarylate that have improved softening characteristics, to making and using hot-mix pavements containing such fibers for paving and repairing geoways (e.g., roadways and runways), and to the geoway structures so made and repaired.
2. The State of the Art.
In the paving and repairing of synthetic load-bearing vehicular geoways, such as roadways, aircraft and aeronautic takeoff/landing runways and launch pads, and similar surfaces, an asphalt cement (i.e., pure asphalt) is typically used as a base material. Asphalt cement is comprised of asphalt and/or bitumen combined with flux oil (i.e., oil obtained from asphalt-base petroleum, typically 20.degree.-25.degree. Be). The asphalt cement is typically mixed with coarse graded mineral aggregate, such as broken stone, slag, or gravel mixed with sand, to produce an asphalt concrete used as the commonly recognized roadway surface. Asphalt-type cement compositions typically contain asphalt cement, rubber, or mixtures of asphalt cement with rubber and/or acrylic copolymers, and asphalt-type concrete compositions contain an asphalt-type cement and aggregate materials. The superambient softening temperature of the asphalt cement in the asphalt concrete requires that the concrete be processed to an elevated temperature to allow its flowable application to the surface being paved or repaired.
Polymeric fibers have been used, among other applications, for the reinforcement of engineering compositions having a variety of utilities. Asphalt-type pavements frequently contain synthetic polymeric staple fibers to improve flexibility and durability of the pavement. For instance, Duszak et al., in U.S. Pat. No. 4,492,781 (the disclosure of which is incorporated herein by reference), describe a fiber-reinforced asphalt-type pavement comprising an emulsifying agent, a water-soluble polymer, and 0.25% to 10% of reinforcing fibers, such as polyethylene or polypropylene staple fiber about 0.1 to 20 mm long, as well as conventional aggregate and thickening and curing agents, for application to surfaces as a hot mixture or as an emulsion. Either hot-mix or emulsified asphalt-type pavements may be applied as a filler for underlying cracks in the surface as a waterproof layer between old and new pavements, or as an external surfacing material. Those different functions involve differences in the amount and fineness of aggregate, the concentration and length of the reinforcing fibers, and the use of different and various conventional additives.
Synthetic staple fibers such as polypropylene and polyethylene fibers are desirable because they are compatible with asphalt-type pavements. The longer lengths and higher concentrations of reinforcing fibers that facilitate interconnections between the fiber and the asphalt matrix, and an increase in durability, nevertheless adversely effect the pumpability (flowability) of the pavement and tend to produce clumping of the fibers. The addition of reinforcing fibers also requires a higher processing temperature range than the conventional 140.degree.-150.degree. C. (284.degree.-302.degree. F.) range for convenient hot application.
Fry, in U.S. Pat. No. 4,422,878 (the disclosure of which is incorporated herein by reference), describes asphalt-type pavements containing about 4-10 wt. % of a fibrous filler, about 2.5 to 15 wt. % of a mixture of eighteen-carbon fatty acids, and up to about 30 wt. % rosin.
Leibee et al., in U.S. Pat. No. 4,662,759, and Trimble, in U.S. Pat. No. 4,502,814 (the disclosures of which are incorporated herein by reference), respectively disclose devices useful for admixing reinforcing fibers into an asphalt-type pavement and for the continuous deposition of a fiber- and asphalt-containing pavement.
Modrak, in European Patent Appln. No. 494,326 (the disclosure of which is incorporated herein by reference), describes fiber-reinforced asphalt pavements characterized in that the reinforcing fibers are bicomponent fibers comprising a polyolefin-containing bonding component conjugated with a polyolefin-wettable reinforcing component.
Spreeuwers, H. R., and G. M. W. van de Pol, in "AP-28: A Polymer Blend of Polypropylene and Polyethylene Terephthalate that Offends the Rules" (Polypropylene Fibres and Textiles IV, Fourth International Conf. on Polypropylene Fibres and Textiles, Univ. of Nottingham, 23-25 Sept. 1987), describe fibers derived from films that comprise 80 wt. % polypropylene and 20 wt. % polyethylene terephthalate (PET). These fibers have an elevated melting point by virtue of particular processing conditions; the melting point of pure polypropylene processed under these conditions increased from 162.degree. C. to 168.degree. C., and to 173.degree. C. with the addition of 20% PET.
In U.S. Pat. No. 4,837,387, van de Pol describes a supporting geotextile fabric for bearing bulk material. The fabrics are made from tape or thread yarns (which van de Pol teaches are described in GB 1,559,056) comprised of 75-85% polypropylene and 25-15% polyester (such as PET). Fibrillated yarns and non-fibrillated tape yarns are significantly different from yarns derived from spun fibers. Yarns produced from films or tapes will have at least two flat surfaces, whereas generally a spun fiber is made with a circular or arcuate cross-section. Additionally, fibers made by splitting a film have a non-uniform cross-section (i.e., a non-uniform width), and thus a non-uniform denier. Further, the denier of such fibers is on the order of 200.+-.50 dpf and the fiber has an extremely high surface area. Even further, the surface along which fibrillation is effected is relatively rough, causing the fibers to entangle and clump, a problem which renders the fibers unsuitable for dispersing in a hot-mix pavement.
There is a need for fiber-reinforced asphalt-type pavements that facilitate the reinforcing integrity of the fibers at the elevated processing temperatures required for application of a hot-mix pavement. There is a need to enhance the fiber integrity and improve durability, flexibility, and shear resistance of the pavement without resorting to increasing the staple length or the concentration of staple fiber. There is also a need for a hot-mix pavement with polymeric reinforcing fibers that can be processed under a wide range of temperature conditions.